Male monkey cares for dying partner
A wild male marmoset has been seen and filmed embracing and caring for his dying partner.
The female accidentally fell from a tree in the forests of Brazil and the male comforted her as she lay dying.
Such behaviour is "astounding", say scientists, having only been previously recorded in primates among chimpanzees and humans.
The marmosets were the dominant pair in their group, having been committed partners for three-and-a-half years.
Within months of the female's death, the male left the group, never to return.
Details of the extraordinary interaction are published in the journal Primates, along with a video recording the behaviour.
End Quote Primatologist Ms Bruna Bezerra of the University of Bristol, who witnessed the encounter
His gentle care and attention towards her left me astounded”
Primatologists spotted the two monkeys while observing common marmosets living in a fragment of Atlantic forest in northeast Brazil.
The team, including Dr Bruna Bezerra of the University of Bristol, UK and colleagues at the Federal Rural University of Pernambuco, in Recife, Brazil, had been studying the same group of common marmosets for a number of years.
They could identify all 12 individuals as well as the monkeys' relationships to each other. The group contained four adult males, three adult females, three juveniles and two infants.
While observing the monkeys the scientists saw the group's dominant female, which they called F1B, fall from a tree, hitting her head on an object on the ground.
Fatally wounded, F1B lay in agony on the ground for two-and-a-half hours before passing away.
"The most remarkable behaviour during this time came from the dominant male M1B," the researchers report.
After 45 minutes, the male noticed the female lying on the floor.
"He immediately went to her," Dr Bezerra told BBC Nature.
The male left behind two babies he had been caring for in the tree, descended to his partner, and embraced her.
He sat alongside her, trying to interact with her, for the next hour and 48 minutes, said Dr Bezerra.
Over the course of her demise, he hugged and sniffed her.
He also kept a look-out, shooing younger members of the group away from his partner's body, gently mobbing the juveniles that tried to approach F1B on the ground.
"When I observed the dominant male approach the dying female, his gentle care and attention towards her left me astounded," said Dr Bezerra.
Researchers have previously witnessed chimps compassionately caring for fellow group members that are dying.
In one example, when a female had been attacked by a leopard, an older chimp similarly kept juvenile members of the group away from her.
Why some nonhuman primates prevent youngsters from approaching dying or dead group members is unclear. Juvenile marmosets are known to care for and groom injured relatives.
The researchers caution that the rarity and complexity of such observations makes it very difficult to evaluate how nonhuman primates perceive death.
For example, during the interaction, M1B tried to copulate with F1B.
Marmosets often use sex to reinforce their social bonds, as do other primates such as bonobos.
As he comforted her, the male also called out, using an alarm call marmosets usually make when they spot an aerial predator such as a bird of prey. But no such predator was in the area, according to the scientists present.
It is unclear whether the sexual aspect of the male's interaction with his partner, or his alarm calls, were made due to grief or the stressful nature of the situation.
"The stressful situation could be the cause of the 'out of context' behaviours performed by the male," Dr Bezerra told BBC Nature.
"However, we could also speculate that the behaviours could have been made to trigger a response from the injured female."
After he comforted the female, her body eventually went into spasm before she died.
Common marmosets live for around a decade, and the male and female had been been together for at least a third of this time.
They had already raised eight offspring between them.
The researchers suspect the female may have been pregnant with more of the male's babies at the time of her death.
Within three months of her passing, the male marmoset left the group, his own fate unknown.
"The dominant male disappeared following the loss of the dominant female," said Dr Bezerra.
"It is all very speculative, but in humans, mortality and illness seem to increase considerably shortly after the loss of a long-term companion. Emotional stress and grief contribute towards poor health and mortality in the bereaved.
"The dominant male had no apparent physical injuries prior to or immediately after the dominant female's death.
"It is possible that at least some of the factors that contribute to mortality in humans after the death of a companion may have similarly affected the dominant male. The male lost the support of its dominant female."